Proving Nontrivial Topology of Pure Bismuth by Quantum Confinement

TL;DR

This study uses quantum confinement and high-resolution spectroscopy on ultrathin Bi films to definitively demonstrate the nontrivial topological nature of pure bismuth, resolving longstanding controversy.

Contribution

It introduces a quantum-confinement approach combined with phase analysis to conclusively determine the topological properties of pure bismuth.

Findings

Observation of quantized bulk bands with ~10 meV energy separation

Unambiguous evidence of nontrivial topological surface states

Validation of quantum confinement as a tool for topological analysis

Abstract

The topology of pure Bi is controversial because of its very small ($\sim$10 meV) band gap. Here we perform high-resolution angle-resolved photoelectron spectroscopy measurements systematically on 14$-$202 bilayers Bi films. Using high-quality films, we succeed in observing quantized bulk bands with energy separations down to $\sim$10 meV. Detailed analyses on the phase shift of the confined wave functions precisely determine the surface and bulk electronic structures, which unambiguously show nontrivial topology. The present results not only prove the fundamental property of Bi but also introduce a capability of the quantum-confinement approach.